Method for improving mechanical properties of polymer particles and its applications

ABSTRACT

A method for improving the mechanical hardness of polymer particles is provided, the method comprising subjecting the polymer particles to a thermal cycle of heating and subsequently cooling. The method is applicable for use with combinations of preferably three monomers, the monomers having hydrophilic and hydrophobic groups in their polymer chain in order to achieve preferential orientation of the polymer chains in a polar solvent after applying the heating cycles of the invention (for example, but not limited to, polymethylmethacrylate and polystyrene based terpolymers and copolymers). Polymeric abrasives used in slurry compositions for polishing copper and their use in a chemical mechanical polishing method are also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.provisional application Ser. No. 60/763,273, filed Jan. 30, 2006, andclaims the benefit under 35 U.S.C. § 119(a)-(d) of European applicationNo. 06119423.9, filed Aug. 23, 2006, the disclosures of which are herebyexpressly incorporated by reference in their entirety and are herebyexpressly made a portion of this application.

FIELD OF THE INVENTION

The preferred embodiments relate to the field of polymer-basedparticles. More specifically they relate to a method to alter themorphological and mechanical properties of polymer particles and itsapplications.

The preferred embodiments further relate to the field of semiconductorprocessing. More specifically they relates to the chemical mechanicalpolishing (CMP) process using polymer particles as abrasive particles.

BACKGROUND OF THE INVENTION

Integration of copper into an IC manufacturing process can beimplemented by using dual damascene processing, in which ChemicalMechanical Polishing (CMP) has been used to remove the overburdenmaterial and planarize the wafer surface.

CMP is the best approach for copper interconnects layers to obtainglobal planarization, while the slurry is the most important andcritical factor in the polishing process. The slurry for copper CMP iscomposed of abrasive particles and chemicals such as inorganic ororganic acids, corrosion inhibitors, oxidizers and complexing agents.The inorganic particles used such as abrasives have high removal rate(RR), but they are hard and they can create many scratches and damagesnot only on copper but also on the silica film surface.

SUMMARY OF THE INVENTION

In order to fully planarize soft materials it is necessary to developnew abrasive particles polymer-based particles.

Untreated polymer abrasives have been tested for resist polishing, buttheir removal rate as such for other materials such as copper and low-kmaterials that are harder than polymeric resist, is not enough.Additions of aggressive chemicals such as oxidizing agents to help theremoval of these harder materials and higher down force can improve thepolishing process but leads to more defectivity such as corrosion (formetals) and mechanical damage. The use of a harder pad in combinationwith the chemicals can improve the removal efficiency but is preferablyavoided for easy damageable surfaces.

To solve these shortcoming of polymer particles, so called compositeabrasives have been developed whereby the polymer particle (core) iscoated with an inorganic silica shell to improve the hardness of theabrasive. The polymer core gives the advantage of being compressible. Anexample of the composite abrasives is described in US 2004/0144755. Thepolymer core of the composite abrasives creates a cushion effect atareas of high local down-force; however the presence of the inorganicshell can still create scratches on easy damageable surfaces such ascopper and low-k materials commonly used in semiconductor processing.

Another approach could be increasing the down force on the wafercarrier, in order to increase material removal rates but this is likelyto cause damages, scratches, delamination or destruction of materiallayers on the wafer, which is especially the case for low-k dielectricmaterials.

Accordingly, it is desirable to solve the shortcomings of the commercialavailable polishing slurries containing polymer particles by improvingthe mechanical properties of the polymer particles, which makes itpossible to polish e.g. Cu structures in semiconductor devices avoidingdamage.

It is also desirable to provide a method to alter the structure ormorphology of polymer based particles, or in other words, altering themacromolecular and supra-molecular structure of polymer particles.

The preferred embodiments relate to a method to increase the mechanicalhardness of polymer particles, the polymer particles comprisinghydrophilic and hydrophobic groups, comprising the step of submittingthe particles contained in a polar solvent, to a thermal cycleconsisting of at least one heating step followed by at least one coolingstep.

In a preferred embodiment, the polymer particles are preferablycopolymer and/or terpolymer particles.

Preferably, the temperature is provided such that the glass transitiontemperature ((Tg)) of the copolymer or terpolymer particles is reached,and even more preferably exceeded, during the at least one heating step.The temperature can be up to maximum 300° C. during the at least oneheating step and down to minimum 10° C. during the at least one coolingstep. Preferably the temperature is up to maximum 200° C. during the atleast one heating step and down to minimum 20° C. during the at leastone cooling step.

In a preferred embodiment, the thermal cycle can be performed in aclosed reactor to avoid evaporation of the solvent.

Preferably, the temperature is increased at a rate of 5° C. per minuteto 10° C. per minute during the at least one heating step.

Preferably, the temperature is decreased at a rate of 15° C. per minuteto 30° C. per minute during the at least one cooling step.

In a preferred embodiment, the polar solvent is preferably water.

The polymer particles can comprise (or consist of)polymethylmethacrylate, polystyrene, polypropylene, polyvinylchloride,polyisobutylene and/or acrylate.

Preferably, the polymer particles comprise (or consist of)methylmethacrylate and methoxypolyethylenglycol-methacrylate.

More preferably, the polymer particles are terpolymer particlesconsisting of methylmethacrylate, methoxypolyethylenglycolmethacrylateand 4-Vinylpyridine.

A method according to a preferred embodiment can further comprise, afterthe thermal cycle, a step of coating the copolymer and/or terpolymerparticles with an inorganic shell or compound.

Preferably, the inorganic shell is silica.

In a preferred embodiment, a polymer particle is provided, moreparticularly a copolymer or a terpolymer particle, obtainable by amethod according to preferred embodiments.

The copolymer or the terpolymer particle can exhibit an elastic moduli(E) (higher than 4 GPa and a hardness higher than 0.25 GPa.

The elastic moduli (E) is determined from nanoindentation measurementsmade by means of a nanoindenter or by atomic force microscopy (AFM));and the hardness is measured by means of a nanoindenter.

Also provided is a polishing slurry composition for use in chemicalmechanical polishing, comprising polymer particles obtainable by amethod according to a preferred embodiment.

The polymer particles obtainable can be used as abrasive particles,either in dry state or in wet state.

The polymer particles obtainable by a method according to the preferredembodiments can be used for polishing layers of semiconductor devices,such as copper layers, low-k dielectric layers (i.e. layers ofdielectric constant k lower than 3,9), photosensitive layers, orsemiconductor wafer substrates.

BRIEF DESCRIPTION OF THE DRAWINGS

All drawings are intended to illustrate some aspects and embodiments ofthe present invention. Not all alternatives and options are shown andtherefore the invention is not limited to the content of the givendrawings.

FIG. 1A (PRIOR ART) illustrates the synthesis of PMMA-based terpolymerparticles used as starting point for further synthesis of the polymerparticles of the preferred embodiments.

FIG. 1B (PRIOR ART) illustrates the synthesis of composite abrasivepolymer particles having a polymer core and silica shell with asilane-coupling agent at the interface.

FIG. 2 shows differential scanning calorimetry (DSC) curves ofmethylmethacrylate (MMA)—methoxypolyethylene glycol methacrylate(MPEGMA)—4-Vinylpyridine (4-ViPy) terpolymer with ratio 15/1/1 (TER-P)in a dry powder formulation.

FIG. 3 shows differential scanning calorimetry (DSC) curves ofmethylmethacrylate (MMA)—methoxypolyethylene glycol methacrylate(MPEGMA)—4-Vinylpyridine (4-ViPy) terpolymer with ratio 15/1/1 (referredto as “TER-P”) in water after the thermal treatment of the preferredembodiments.

FIG. 4 shows differential scanning calorimetry (DSC) curves ofmethylmethacrylate (MMA)—methoxypolyethylene glycol methacrylate(MPEGMA) copolymer (referred to as “CO-P”) in water.

FIG. 5 shows differential scanning calorimetry (DSC) curves ofmethylmethacrylate (MMA)—methoxypolyethylene glycol methacrylate(MPEGMA)—4-Vinylpyridine (4-ViPy) terpolymer synthesized in presence ofthe cationic surfactant cetyltrimethylammonium hydrogen sulfate (CTAHS)(referred to as “TER-P-S”) in water.

FIG. 6A shows differential scanning calorimetry (DSC) curves of “TER-P”with a continuous “raspberry-like” coating made by silica particles(diameter=30 nm) achieved with silane coupling agent at the interfacebetween the core and the shell (referred to as “TER-C-A”) in water.

FIG. 6B shows differential scanning calorimetry (DSC) curves of “TER-P”with a continuous “raspberry-like” coating made by silica particles(diameter=30 nm) achieved without silane coupling agent at the interfacebetween the core and the shell (referred to as “TER-C-B”) in water.

FIG. 7A illustrates the material's modulus (E) from nanoindentationmeasurements of a particle layer of about 1 micron for indentation depthof 500 nm (plastic deformation). There is clearly an improvement of theE value from 3 GPa (untreated TER-P) to 7 GPa (treated TER-P).

FIG. 7B illustrates the hardness (H) of the material fromnanoindentation measurements of a particle layer of about 1 micron forindentation depth of 500 nm (plastic deformation). There is clearly animprovement of the material's H value from 0.08 GPa (untreated TER-P) to0.25 GPa (treated TER-P).

FIG. 8A illustrates a Force-indentation curve for a TER-P sample aftertreatment in air measured by AFM. FIG. 8B illustrates aForce-indentation curve after treatment for a TER-P sample in watermeasured by AFM. FIG. 8C illustrates a Force-indentation curve fornon-treated TER-P samples and composite polymer particles in airmeasured by AFM. FIG. 8D illustrates a Force-indentation curve fornon-treated TER-P samples and composite polymer particles in watermeasured by AFM. FIG. 8E illustrates calculated elastic moduli (E) fromnanoindentation measurements by AFM in air vs. water for a TER-P sampleafter a thermal treatment (improvement is indicated with arrow).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments provide a method for improving the mechanicalproperties such as hardness and elastic modulus of polymer particles.

More particularly, a method according to the preferred embodiments forimproving the mechanical properties, in particular the hardness, ofpolymer particles comprises the step of submitting polymer particles,preferably copolymer and/or terpolymer particles, contained in a polarsolvent, the particles comprising hydrophilic and hydrophobic groups, toat least one thermal cycle, each thermal cycle consisting of at leastone heating step followed by at least one cooling step.

A method according to the preferred embodiments allows to improve themechanical properties of polymer particles without (substantially)altering the size and/or shape of the polymer particles.

A method of the preferred embodiments also allows to improve themechanical properties of polymer particles without (substantially)altering the original size distribution of the particles.

In the context of the preferred embodiments, polymer particles can referto homopolymers or heteropolymers.

A copolymer generally refers to the product of polymerization of atleast two different types of monomer, but in the context of thepreferred embodiments, a copolymer refers to the product ofpolymerization of exactly two different types of monomer. A terpolymerrefers to the product of polymerization of exactly three different typesof monomer. The term “heteropolymer(s)” is meant to encompasscopolymers, terpolymers and polymers resulting from the polymerizationof more than three different types of monomer.

In the context of the preferred embodiments, the term “crystalline” withrespect to the polymer particles obtained by a method of the preferredembodiments, refers to a semi-crystalline morphology consisting of(increased) crystalline and amorphous phases. The crystalline phaseconsists in more ordered domains where the polymer chains orientatethemselves in the minimum energy conformation imparting a specifictacticity to the structure.

The polymer particles as described and used in the preferred embodimentsare preferably a combination of two different types of monomer (referredto as copolymer(s)) and/or a combination of three different types ofmonomer (referred to as terpolymer(s)).

The monomers in the polymers, more particularly in the copolymers, or inthe terpolymers, comprise a combination of hydrophobic and hydrophilicgroups.

Preferably, the monomers used in a method according to the preferredembodiments comprise a vinyl group.

Monomers comprised in the polymers, in particular in the copolymersand/or terpolymers, to be used in a method of the preferred embodimentscan be selected from the group consisting of (meth)acrylic acid,acrylamide, methacrylamide, alkyl-(meth)-acrylates having 1 to 24 carbonatoms in the alkyl group, vinyl aromatic monomers (e.g. vinyl pyridine,alkyl vinyl pyridine, vinyl butyrolactam, vinyl caprolactam),monocarboxylic acid, dicarboxylic acid, itaconic acid, substituted vinylaromatic monomers, olefins (e.g. propylene, isobutylene, or long chainalkyl olefins having 10 to 20 carbon atoms), vinyl alcohol esters (e.g.vinyl acetate, vinyl stearate), vinyl halides (e.g. vinyl fluoride,vinyl chloride, vinylidene fluoride), and vinyl nitriles (e.g.acrylonitrile, methacrylonitrile).

A copolymer or a terpolymer to be used in a preferred embodiment canresult from the polymerization of:

-   -   (meth)acrylic acid with acrylamide or methacrylamide,    -   (meth)acrylic acid with styrene or with other vinyl aromatic        monomers,    -   alkyl(meth)acrylates (esters of acrylic or methacrylic acid)        with a mono or dicarboxylic acid, such as, acrylic or        methacrylic acid or itaconic acid,    -   substituted vinyl aromatic monomers having substituents, such        as, halogen (i.e. chlorine, fluorine, bromine), nitro, cyano,        alkoxy, haloalkyl, carboxy, amino, amino alkyl with an        unsaturated mono or dicarboxylic acid and/or an        alkyl(meth)acrylate,    -   monoethylenically unsaturated monomers containing a nitrogen        ring, such as, vinyl pyridine, alkyl vinyl pyridine, vinyl        butyrolactam, vinyl caprolactam, with an unsaturated mono or        dicarboxylic acid;    -   olefins, such as, propylene, isobutylene, or long chain alkyl        olefins having 10 to 20 carbon atoms with an unsaturated mono or        dicarboxylic acid,    -   vinyl alcohol esters, such as, vinyl acetate and vinyl stearate        and/or vinyl halides, such as, vinyl fluoride, vinyl chloride,        vinylidene fluoride and/or vinyl nitriles, such as,        acrylonitrile and methacrylonitrile with an unsaturated mono or        dicarboxylic acid,    -   alkyl(meth)acrylates having 1 to 24 carbon atoms in the alkyl        group and an unsaturated monocarboxylic acid, such as, acrylic        acid or methacrylic acid.

Preferably two or three monomers of different hydrophobicity are used(respectively for a copolymer and a terpolymer to be used in a method ofthe preferred embodiments) in order to have preferential orientations inwater, after the thermal cycle(s), for example, but not limited thereto,polymethylmethacrylate and polystyrene based copolymers and terpolymers.

Preferably, the polymer particles comprise (or consist of)polypropylene, polyvinylchloride, polyisobutylene and/or acrylate.

A preferred copolymer to be used (as starting polymer particles for thethermal cycle(s)) in a method of the preferred embodiments results fromthe polymerization of methyl-methacrylate (MMA) andmethoxypolyethylenglycolmethacrylate (MPGEMA).

A preferred terpolymer to be used (as starting polymer particles for thethermal cycle(s)) in a method of the preferred embodiments results fromthe polymerization of methyl-methacrylate (MMA),methoxypolyethylenglycolmethacrylate (MPGEMA), and vinyl-pyridine (moreparticularly 4-vinyl-pyridine).

A method of the preferred embodiments comprises a thermal treatment,more particularly a thermal cycle consisting of successively heating andcooling. The thermal cycle can comprise (or consist of) at least oneheating step followed by at least one cooling step. The thermal cyclecan comprise (or consist of) one heating step (immediately) followed byone cooling step (immediately) followed by one heating step. Preferably,the thermal cycle comprises (or consists of) one heating stepimmediately followed by one cooling step.

To obtain reorientation within the polymer particles, at least oneheating and cooling cycle is required. Optionally, the heating andcooling cycle (i.e. the thermal cycle) can be repeated once, twice ormore.

The temperature during the heating and cooling procedure variespreferably in the range of minimum 10° C. and maximum 300° C. and morepreferred between room temperature (about 20° C.) and 200° C.

The temperature to be reached during the heating step is preferablyabove the glass transition temperature ((Tg)) of the polymer particles.Tg is the temperature at which an amorphous polymer (or amorphousregions in a partially crystalline polymer) changes from a hard andrelatively stable condition to a viscous or rubbery condition.

The thermal treatment is intentionally applied to give enough thermalenergy in order to overcome the activation energy barrier to achieve adifferent conformation of the polymer chain. The different conformationis preferably a more ordered crystalline structure.

Preferably, the temperature during the heating step reaches the glasstransition temperature (T_(g)) of the copolymers and/or terpolymers; andin case of a mixture of different polymers, the temperature during theheating step preferably reaches at least the lowest T_(g), and morepreferably the highest T_(g). In particular, the temperature used in theheating step is preferably up to maximum 300° C., more preferably up tomaximum 200° C.

Preferably, the cooling step is down to minimum 10° C., more preferablydown to minimum 20° C.

More preferred the thermal cycle comprises one heating step up tomaximum 200° C. followed by one cooling step down to minimum 20° C.

Even more preferably, the thermal cycle comprises one heating stepherein the temperature is raised beyond the Tg of the polymers, moreparticularly of the copolymers and/or the terpolymers, and up to (about)200° C., followed by one cooling step down to the room temperature (i.e.about 20° C.).

During the thermal treatment, the alternating hydrophobic andhydrophilic groups in the individual monomer chains can reorientthemselves in the presence of a polar solvent. The thermal treatment istherefore performed in the presence of a polar solvent (i.e. anysuitable solvent the dipole moment of which is different from and higherthan 0) such that the polymer chains of the individual monomers can bereordered and crystallization of the copolymer or terpolymer basedpolymer particles can take place.

Preferred examples of polar solvents are alcohols (e.g. methanol,ethanol), acetone, and more preferably water.

Preferably, the thermal cycle comprises a slow heating step followed bya rapid cooling step. By slow heating step it is meant heating at a ratecomprised preferably between about 5° C./min and about 10° C./min (lessthan 5° C./min, and also 6° C./min, 7° C./min, 8° C./min, 9° C./min, 11°C./min, or 12° C./min being envisaged in a method of the preferredembodiments), to favour the reorientation of the polymer chain.

For an optimal method of the preferred embodiments, the temperaturereached during the heating step should be at least (few degrees, i.e. 1,2, 3, 10, or more) above the glass transition temperature ((Tg)) of thepolymers.

Preferably the slow heating step is followed by a rapid cooling stepsuch that the altered conformation is blocked, the altered conformationis preferably corresponding to a more crystalline state and leading toimproved mechanical properties.

By rapid cooling step is meant cooling at a rate of approximately 15°C./min up to 20° C./min. Cooling at a rate of 14° C./min, 16° C./min,17° C./min, 18° C./min, 19° C./min or 21° C./min or more is alsoenvisaged in a method of the preferred embodiments.

A method of the preferred embodiments can also be defined as a methodfor fabricating polymers, more particularly new copolymer and/orterpolymer particles, comprising the step of polymerizing (suitable)monomers as defined herein and the step of submitting the particlesobtained to a thermal cycle as defined herein.

Preferably, the thermal cycle comprises at least one heating stepwherein the temperature is raised beyond the T_(g) of the polymerparticles obtained in the previous step, followed by at least onecooling step wherein the temperature is decreased down to the roomtemperature (i.e. about 20° C.).

More preferably, the thermal cycle consists of one heating step, whereinthe temperature is raised beyond the T_(g) of the polymer particles,preferably at a rate of less than about 10° C./min, and one coolingstep, wherein the temperature is decreased down to room temperature,preferably at a rate of more than about 15° C./min.

The polymer particles of the preferred embodiments have severaladditional advantages compared to untreated polymer particles such asstability towards pH.

To stabilize the polymer particles of the preferred embodiments insolution, no surfactant needs to be added.

Addition of cationic surfactant even in very low concentration (traceamount), leads to polymer particles with a positive zeta potential suchthat the influence of pH (or in other words change in pH) has a greatimpact on the behavior of the particles.

The method of the preferred embodiments does not need the use ofsurfactants during synthesis or treatment because monomers are chosenwith altering hydrophilic and hydrophobic groups. The obtained (treated)polymer particle itself acts as a micelle-like structure.

In accordance with a method of the preferred embodiments, the thermalcycle of heating and cooling offers advantages in respect to known stateof the art processes used for improving the mechanical properties of theparticles (such as elastic modulus or hardness) which may change thesize, size distribution or shape of the particles. For example, using across-linker during the synthesis makes it very difficult to achievehigh monodispersity in the particle size.

To the contrary, a method of the preferred embodiments makes it possibleto achieve a high monodispersity in particle size of the particlesobtained.

The high monodispersity preferably refers to particles having a standarddeviation on the average size (or diameter) of about 5-10%. In otherwords, the particles preferably exhibit uniformity in size (or diameter)of more than about 90% and more preferably of more than about 95%.

The size of the polymer particles obtained by the preferred embodimentscan span from hundreds of nanometers to microns.

During the thermal treatment/cycle(s) of the preferred embodiments, theinitial size (distribution) of the polymer particles is notsubstantially altered.

The initial size of polymer particles can however be tuned duringsynthesis by parameters such as the monomer content, synthesistemperature and the type of initiator.

Different types of polymer particles can be used in a method accordingto the preferred embodiments to obtain the polymer particles of thepreferred embodiments.

Preferably the starting polymer particles are made of copolymers and/orterpolymers wherein the monomers comprise hydrophilic and hydrophobicgroups.

Rising the temperature during the heating phase/step gives the necessaryenergy to overcome the activation barrier for the rotation andreorganization of the polymer chains; and in the rapid cooling phase thereorganization is immobilized towards the actual energetically morestable conformation.

The effect of reorganization of the chains within the polymer particlesduring the thermal treatment is only possible in the presence of a polarsolvent, preferably water, because of its specific interactions with thehydrophilic groups of the individual monomers constituting the polymerparticles. The interaction leads to a reorientation of the groupstowards the polar solvent and hence towards the external side of thepolymer particle.

It has been observed that the polymer particles obtained by a methodaccording to the preferred embodiments (and also an advantage of one ormore preferred embodiments) exhibit a semi-crystalline morphologyconsisting of crystalline and amorphous phases. The crystalline phaseconsists in more ordered domains where the polymer chains orientatethemselves in the minimum energy conformation imparting a specifictacticity to the structure.

The mechanical properties of the polymers are largely determined bytheir degree of crystallinity and by the orientation of the chains inthe polymers.

In the preferred embodiments the re-orientation of the polymer chains isachieved by the interactions of the polymer chains with the solventmolecules during the thermal treatment/cycle. Indeed, the polarity (orhydrophilicity) of the solvent is important to induce interactions withthe hydrophilic segments of the polymer. A preferred example of a polarsolvent to be used is water. Further examples of polar solvents arealcohols such as methanol and/or ethanol.

The polymer particles of the preferred embodiments can be coated with aninorganic compound to obtain composite polymer particles.

The polymeric particles (in particular the copolymers and/or terpolymersand also the composite polymeric particles) of the preferred embodimentscan be used as abrasives (also referred to as polymeric abrasives) forchemical mechanical polishing (CMP).

The composite polymeric particles, the copolymers and/or terpolymers,obtained by a method of the preferred embodiments are particularlysuitable for easily damageable surfaces such as copper and low-kmaterials (i.e. dielectric constant k lower than 3.9).

The polymeric particles of the preferred embodiments present bettermechanical properties compared to inorganic hard abrasives such assilica, alumina or ceria.

The micromechanical processes of deformation occurring in response to anexternal mechanical load, such as the down force acting during the CMPprocess, are much more flexible for polymeric abrasives of the preferredembodiments compared to hard inorganic abrasives, conferring to polymerparticles of the preferred embodiments strong advantages for someapplications such as CMP, compared to state of the art particles.

The polymeric abrasives of the preferred embodiments can be used inpolishing slurry.

The polishing slurry is also provided in preferred embodiments.

A polishing slurry of the preferred embodiments can further comprise anysuitable compound(s) or additive(s) known from the skilled person, suchas oxidizing agents, anti-corrosive agents, and/or surfactants.

Alternatively, the polymer particles (or polymer abrasives) of thepreferred embodiments can be added to an existing commercially availableCMP polishing slurry for improving the performance of the slurry.

Alternatively chemicals such as oxidizers can be encapsulated within thecore of the polymer particles such that during down force on theseparticles, e.g. during the CMP process, these chemicals are graduallyreleased.

The polymer particles of the preferred embodiments can also be usedwithin a post-CMP cleaning solution or post-CMP cleaning slurry.

The post-CMP slurry or post-CMP solution (also an advantage of at leastone preferred embodiment) can be applied after the (Cu) CMP process.

A post-CMP cleaning solution or post-CMP cleaning slurry according tothe preferred embodiments can be used to remove remaining and/orunwanted products after a CMP process.

A Cu-CMP process is normally performed on a multi-platen CMP tool tooptimize the throughput and planarity of the wafers. The first platen isused primarily for removal of the unwanted Cu above the patterned andetched features. Once the bulk material has been removed, the wafers aretransferred to Platen 2 where the residual (Cu) and barrier metal areremoved simultaneously using a non-selective slurry. Finally, the wafersare subjected to a buffing step on platen 3 to smooth the surface, aswell as to remove any remaining barrier metal. This CMP's subsequentrinsing and buffing step is aimed at minimizing micro-scratch generationand increasing the planarity. The applied down force in this case isvery low and a soft pad is preferably used.

A soft polymer-based slurry (a slurry comprising polymer particlesaccording to the preferred embodiments) shows enhanced removal rate withrespect to a conventional post CMP cleaning slurry, resulting in asubstantial improvement of this final buffing step.

According to a preferred embodiment, terpolymer particles (also referredto as “TER-P”) resulting from the polymerization of methylmethacrylate(MMA), methoxypoly-ethylenglycolmethacrylate (MPEGMA) and4-Vinyl-pyridine (4ViPy) are used as starting polymers in a methodaccording to the preferred embodiments.

The ratio of MMA/MPEGMA/4-ViPy can be respectively from 2/1/1 to 30/1/1.

Preferably, the ratio of MMA/MPEGMA/4-ViPy is respectively 15/1/1.

Alternatively and also preferred, copolymer particles resulting from thepolymerization of MMA and MPEGMA monomers can be used as startingpolymer particles of a method according to the preferred embodiments.

The preferred terpolymer and copolymer particles show during the thermaltreatment/cycle, in water, an additional shoulder in the heat capacityat approximately 130° C., shortly above their glass transitiontemperature (T_(g)).

The thermal treatment in a method of the preferred embodiments generatesan increase of the crystallinity of the polymer particles due to are-orientation of the polymer chains. The hydrophilic groups orientatetowards the polar molecules of the polar solvent, and the thus obtainedre-orientation is a more ordered structure leading to a more crystallinestructure with increased mechanical properties. Indeed, mechanicalproperties of the polymer particles are largely determined by the degreeof crystallinity present in the polymer particles and by the orientationof the polymer chains in the polymer particles.

Differential scanning calorimetry (DSC) can be used to perform thethermal treatment and analysis of the polymer particles of the preferredembodiments on a lab scale.

Other techniques can be used to perform the thermal treatment on largerscale such as closed reactors with temperature control that canwithstand the pressure build up during heating.

DSC curves established for the TER-P polymer particles in a dry state(dry powder formulation) are shown in FIG. 2. No crystallization of theTER-P polymer particles can be observed after a thermal cycle consistingof a heating step from 25° C. to 200° C. at 10° C./min, followed by acooling step from 200° C. to 25° C. at 10° C., followed by a secondheating step from 25° C. to 200° C. at 10° C./min.

In FIG. 3, DSC curves are established for the TER-P polymer particles incolloidal solution (or in other words having the polar solventavailable). FIG. 3 shows a crystallization exothermic peak at 130° C.during the same thermal cycle as applied for FIG. 2.

In other words, crystallization occurs only for the TER-P polymerparticles having the polar solvent (water) present in the pan. And wherethere is no solvent available in the DSC pan (dry polymer particles)during the thermal treatment (and measurement) no reordering of thepolymer chains occurs.

To a minor extent, the same effect of crystallization can be observed inthe curve for the CO-P polymer particles in water, submitted to athermal cycle as shown in FIG. 4; and no effect of crystallization isobserved in the presence of surfactant as shown in FIG. 5.

There is no crystallization observed when the polymer particle (core) iscoated by a silica shell and then submitted, in water, to a thermalcycle, as shown in FIG. 6A (for the TER-C-A) and FIG. 6B (for theTER-C-B).

The polymer particles obtained after the thermal cycle(s) of heating andcooling can find application in the challenging chemical mechanicalplanarization (CMP) of softer and easily damageable new materials, suchas Cu and Low-k materials, introduced in the integrated circuit (IC)manufacturing industry.

The polymer particles of the preferred embodiments are preferably usedto tune the polishing mechanism in order to be less mechanical (or inother words more compressible after using a down force) compared to thecurrent state of the art CMP processes involving inorganic hardabrasives such as silica, alumina or ceria.

For use in Chemical Mechanical Polishing, the polymer particles of thepreferred embodiments having a reorganized structure after thermaltreatment can be used as such or added to a polishing slurry.

The polymer particles are preferably used in the presence of a solventor in other words in a “wet” state or as a water-based composition sincethe mechanical properties are then maximally enhanced.

The polishing slurry is preferably used for polishing copper and/oreasily damageable surfaces on semiconductor substrates.

Additives such as oxidizing agents and/or surfactant and/oranti-corrosive agents can be further added to the polishing slurry toimprove the performance of the slurry.

In an alternative and also preferred embodiment, the polymer particlesof the preferred embodiments can be further coated with an inorganiccoating, the coating being performed after the thermal treatment.

For example the “TER-P” polymer particles can be coated with acontinuous “raspberry-like” coating made by silica particles(diameter=30 nm). This coating can be achieved with (referred to as“TER-C-A”) and without (referred to as “TER-C-B”) silane coupling agentat the interface between the core (polymer) and the shell (silica).

Copolymer and/or terpolymer particles obtained by a method according tothe preferred embodiments, in a dry state (i.e. no solvent present),exhibit an elastic moduli (E) higher than 6 GPa and a hardness higherthan 0.25 GPa. More particularly, the particles exhibit an elasticmoduli (E) comprised between about 6 GPa and about 10 GPa, and ahardness comprised between about 0.25 GPa and about 1 GPa.

In a wet state, the copolymer and/or terpolymer particles exhibit anelastic moduli (E) higher than 4 GPa and a hardness higher than 0.25GPa. More particularly, the particles exhibit an elastic moduli (E)comprised between about 4 GPa and about 10 GPa, and a hardness comprisedbetween about 0.25 GPa and about 1 GPa.

The hardness (H) has been determined using nanoindentation measurementsby means of a nanoindenter.

The elastic moduli (E) has been determined using nanoindentationmeasurements by means of a nanoindenter or by AFM (Atomic forcemicroscopy) process.

Nanoindentation measurements refer to a technique similar toconventional hardness testing but performed on a much smaller scale. Theforce required to press a sharp diamond indenter into a material ismeasured as a function of indentation depth. As depth resolution is onthe scale of nanometers (hence the name of the instrument), it ispossible to conduct indentation experiments even on thin films. Twoquantities, which can be readily extracted from nanoindentationexperiments, are the material's modulus E and its hardness H, which canbe correlated to yield strength.

EXAMPLES

Materials used in the following examples are Methyl methacrylate (MMA,99% purity, Aldrich), Methoxypolyethylene glycol methacrylate (MPEGMA),average molecular weight 454, Aldrich), 4-Vinylpyridine (4-ViPy, 95%purity, Aldrich), 2,2′-Azobis(2-methylpropionamidine) dihydrochloride(97%, Sigma-Aldrich), 4-Vinylpyridine (95% purity, Aldrich). Thesematerials were used as received, without further purification.

pH solutions were prepared using HCl, NaOH, and NaCl (of analyticalgrade received from Wako Chemical Co.) in a concentration of 10-3 M as abackground electrolyte.

Example 1 Preparation of Polymer Particles as Starting Point

Poly-methylmethacrylate (PMMA)-based spheres were synthesized by asurfactant-free radical free polymerization, using a modification of theprocedure described by K. Nishimoto et al. (U.S. Pat. No. 6,582,761).

A typical polymerization procedure was as follows: Methyl methacrylate(MMA), Methoxypolyethylene glycol methacrylate (MPEGMA), andion-exchanged water (DIW) were charged in a round-bottomed three-neckedflask.

In order to prevent aggregation of the particles, a third co-monomer4-Vinylpyridine (4-ViPy) was added to the system. This solution washeated to 70° C. while stirring.

Afterwards the aza-type polymerization initiator2,2′-Azobis(2-methylpropionamidine) dihydrochloride (pre-dissolved inwater) (APDH) was added to the reaction.

Before the process was initiated, i.e. monomer is added, to eliminatethe effects of oxygen, the solution was purged with nitrogen and thereaction was carried out under nitrogen gas atmosphere, until theconversion exceeded 80%-90%, as determined thermo-gravimetrically.

Finally, the system was quenched in a cold-water bath to discontinue thereaction.

The final size of the polymer particles was 367±15 nm (determined byScanning Electron Microscopy as an average of 100 measurements) and494±59 nm (determined by Dynamic Light Scattering in water).

Example 2 Post Synthesis Treatment

The dispersions resulting from the synthesis presented in example 1 werecentrifuged, the supernatant solutions discarded, and the particlesre-suspended in deionised water using ultrasonic treatment. This processwas repeated 3 times.

The treatment gave PMMA nanoparticles with positive surface charge (ζpotential).

The centrifuge/ultrasound cycle is needed for the purification of theparticles. The positive surface charge helps the electrostaticstabilization of the particles in solution. More than a reorderingoccurring during ultrasound treatment the particles are re-dispersed inorder to be kept far enough from each other avoiding any agglomeration.

Example 3 Thermal Treatment of Polymer Particles

The thermal treatment method of heating and subsequent cooling ismonitored and performed on a Differential Scanning Calorimeter (DSC).

The DSC tool is a thermal analysis instrument that determines thetemperature and heat flow associated with material transitions as afunction of time and temperature.

The thermal cycle can give information about the percent ofcrystallinity and the crystallization kinetics and phase transition of amaterial.

In a heat flux DSC, the sample material, enclosed in a pan and an emptyreference pan are placed on a thermoelectric disk surrounded by afurnace. The furnace is heated at a linear heating rate and the heat istransferred to the sample and reference pan through thermoelectric disk.However owing to the heat capacity of the sample there exists atemperature difference between the sample and reference pans which ismeasured by area thermocouples and the consequent heat flow isdetermined by the thermal equivalent of Ohm's law:q=ΔT/R, wherein q isthe sample heat flow, ΔT, temperature difference between sample andreference, and R, resistance of thermoelectric disk.

The main operations for the measurement are:

-   -   calibrating the instrument with Indium and benzophenone of known        masses,    -   selecting the pan type and material,    -   preparing the sample,    -   creating or choosing the test procedure and entering sample and        instrument information through the TA instrument control        software,    -   setting the purge gas flow rate,    -   loading the sample and closing the cell lid,    -   starting the experiment.

For each sample as a solid powder or aqueous colloidal solution thethermal cycle was repeated 2 times. For the study of aqueous solutionsabove 100° C. hermetic pans were the best choice.

Generally the appropriate mass range for samples in DSC is 1 mg to 10mg. About 10 mg of solid compounds and 5 wt. % aqueous solutions wereused.

An example of the thermal cycle is as follows:

1) Hold for 5 min at 25° C.,

2) Heat from 25C to 200° C. at 10C/min,

3) Hold for 5 min at 200° C.,

4) Cool from 200 C to 25° C. at 15° C./min,

5) Hold for 5 min at 25° C.,

6) Heat from 25 C to 200° C. at 10° C./min,

7) Hold for 5 min at 200° C.,

8) Cool from 200° C. to 25° C. at 15° C./min.

During the thermal heating, the sample preferably remains in a thermalequilibrium, to achieve the thermal equilibrium the heating rate ispreferably as slow as possible.

Example 4 Preparation of the Composite Particles

Starting from PPMA nanoparticles obtained with the method of thepreferred embodiments to improve the mechanical properties (thermaltreatment as described in example 3), composite particles comprisingsilane-coupling agents between (polymer) core and (silica) shell can beprepared as follows.

An aqueous dispersion containing the PMMA-based particles as previouslysynthesized was charged in a round-bottomed three-necked flask,(chloromethyl) trimethylsilane was added, and the mixture was stirred atlow pH.

This first step leads to an aqueous dispersion of silanized PMMA-basedparticles that could be added to a colloidal silica particle suspension,to obtain a dispersion of particles in which silica particles hadadhered to the polymer ones.

To achieve this, an aqueous dispersion containing the colloidal silicaparticles (pH 8) was added to the former solution. Vinyltriethoxysilanewas added to this aqueous dispersion, the mixture was stirred, and thenTEOS was added, heated to 60° C., stirred, and then cooled in a coldwater bath.

Thus, an aqueous dispersion containing composite particles was obtained.

The final size of the composite particles (silica shell 30 nm diameter)was 453±27 nm (determined by Scanning Electron Microscopy) and 554±67 nm(determined by Dynamic Light Scattering in water).

Alternatively composite particles can be prepared as follows. An aqueousdispersion containing the PMMA-based particles (pH 2) is mixed with anaqueous dispersion containing the colloidal silica, to obtain an aqueousdispersion (pH 5), and the mixture is stirred to obtain an aqueousdispersion containing the composite particles.

The final size of these alternative composite particles (silica shell 30nm diameter) is 440±18 nm (determined by Scanning Electron Microscopy)and 567±64 nm (determined by Dynamic Light Scattering in water).

Example 5 Nanoindentation Measurements on Polymer Particles

In FIG. 7 material's modulus E and its hardness H data are illustratedfrom nanoindentation measurements on a layer comprising the polymerparticles, the layer having a thickness of about 1 micron (achieved bymeans of a stapling of the polymer particles) for indentation depth of500 nm (plastic deformation).

The material's modulus E and its hardness H can be correlated to yieldstrength.

There is an improvement of the E value from 3 GPa for untreated TER-Ppolymer particles towards 7 GPa for TER-P polymer particles afterthermal treatment of the preferred embodiments.

The hardness (H) value shifted from 0.08 GPa for the untreated TER-Ppolymer particles towards 0.25 GPa for thermal treated TER-P polymerparticles as indicated in FIG. 7B.

FIG. 8 illustrates AFM nanoindentation measurement results performedtechnique allowed lower indentation depths (below 50 nm) on aTER-P-treated particle monolayer deposited on newly cleaved micasubstrate. The measurements were carried out in air and in water.

FIG. 8A illustrates a Force-indentation curve for a TER-P sample aftertreatment in air measured by AFM.

FIG. 8B illustrates a Force-indentation curve for a treated TER-P samplein water measured by AFM.

FIG. 8C illustrates the Force-indentation curves for untreated TER-P andcomposites TER-C-A and TER-C-B in air measured by AFM as a comparison.

FIG. 8D illustrates the Force-indentation curves for untreated TER-P andcomposites TER-C-A and TER-C-B in water measured by AFM as a comparison.

The E value (illustrated in FIG. 8E) calculated from theforce-indentation curves for treated TER-P samples in water is 4 GPa, inair (dried state after removal of the solvent) it is 6,5 GPa. It isknown that solid-state particles are harder compared to wet particles.For the untreated TER-P—particles the E value in water is 1.6 and thereis of course also an increase of the E value from 1,6 GPa to 4 GPa indried state (in air).

To extract quantitative values of Young's modulus from theforce-indentation curves, the classical Hertzian contact models can beused from the continuum mechanics of contacts:

E ₂=[3F(1−ν₂ ²)/4δ^(3/2)][(R ₁ +R ₂)/R ₁ R ₂]^(1/2)

wherein δ is the indentation depth, F is the applied load, R₁ and R₂ arerespectively the radius of curvature of the spherical or parabolicindenter and of the indented particles, and E₂ is the surface elasticmodulus of the particle (considering that the E for the tip is 130-160GPa) and ν₂ is the Poisson ratio of the sample. Because the Poissonratios of the PMMA-based terpolymer (and the composites) are not known,the Poisson ratio of bulk PMMA (ν₂=0.38) was used in the calculations.

All references cited herein are incorporated herein by reference intheir entirety. To the extent publications and patents or patentapplications incorporated by reference contradict the disclosurecontained in the specification, the specification is intended tosupersede and/or take precedence over any such contradictory material.

The term “comprising” as used herein is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps.

All numbers expressing quantities of ingredients, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.” Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe specification and attached claims are approximations that may varydepending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should be construed in light of the number ofsignificant digits and ordinary rounding approaches.

The above description discloses several methods and materials of thepresent invention. This invention is susceptible to modifications in themethods and materials, as well as alterations in the fabrication methodsand equipment. Such modifications will become apparent to those skilledin the art from a consideration of this disclosure or practice of theinvention disclosed herein. Consequently, it is not intended that thisinvention be limited to the specific embodiments disclosed herein, butthat it cover all modifications and alternatives coming within the truescope and spirit of the invention as embodied in the attached claims.

1. A method for increasing a mechanical hardness of polymer particles,the polymer particles comprising hydrophilic groups and hydrophobicgroups, the method comprising the step of: subjecting the polymerparticles to a thermal cycle comprising at least one heating stepfollowed by at least one cooling step, wherein the polymer particles arecontained in a polar solvent, whereby a mechanical hardness of thepolymer particles is increased.
 2. A method according to claim 1,wherein the polymer particles comprise at least one type of particleselected from the group consisting of copolymer particles and terpolymerparticles.
 3. A method according to claim 1, wherein a glass transitiontemperature of the polymer particles is reached or exceeded during theheating step.
 4. A method according to claim 1, wherein the polymerparticles are subjected to a temperature of up to 300° C. during theheating step, and wherein the polymer particles are subjected to atemperature down to 10° C. during the cooling step.
 5. A methodaccording to claim 1, wherein the polymer particles are subjected to atemperature of up to 200° C. during the heating step, and wherein thepolymer particles are subjected to a temperature down to 20° C. duringthe cooling step.
 6. A method according to claim 1, wherein the thermalcycle is performed in a closed reactor, whereby evaporation of thesolvent is substantially avoided.
 7. A method according to claim 1,wherein the polymer particles are subjected to a temperature that isincreased at a rate of 5° C. per minute to 10° C. per minute during theheating step.
 8. A method according to claim 1, wherein the polymerparticles are subjected to a temperature that is decreased at a rate of15° C. per minute to 30° C. per minute during the cooling step.
 9. Amethod according to claim 1, wherein the polar solvent is water.
 10. Amethod according to claim 1, wherein the polymer particles comprise atleast one polymer selected from the group consisting ofpolymethylmethacrylate, polystyrene, polypropylene, polyvinylchloride,polyisobutylene, and acrylate.
 11. A method according to claim 1,wherein the polymer particles comprise at least one polymer selectedfrom the group consisting of methylmethacrylate andmethoxypolyethylenglycolmethacrylate.
 12. A method according to claim 1,wherein the polymer particles comprise methylmethacrylate,methoxypolyethylenglycolmethacrylate and 4-vinylpyridine.
 13. A methodaccording to claim 1, further comprising, after the thermal cycle, astep of coating the polymer particles with an inorganic shell or aninorganic compound.
 14. A method according to claim 13, wherein theinorganic shell is silica.
 15. A polymer particle having increasedmechanical hardness resulting from subjecting the polymer particle, in apolar solvent, to a thermal cycle of at least one heating step followedby at least one cooling step, wherein the polymer particle is acopolymer particle or a terpolymer particle, and wherein the polymerparticle has an elastic moduli higher than 4 GPa and a hardness higherthan 0.25 GPa.
 16. A polymer particle according to claim 15, having anelastic moduli of from 4 GPa to 10 GPa and a hardness of from 0.25 GPato 1 GPa.
 17. A polishing slurry composition for use in chemicalmechanical polishing, comprising a polymer particle according to claim15.
 18. A method of abrading, comprising use of a polymer particleaccording to claim 16 as an abrasive particle.
 19. The method accordingto claim 19, wherein the particle is in a dry state.
 20. The methodaccording to claim 19, wherein the particle is in a wet state.
 21. Themethod according to claim 19, wherein the polymer particle is used as anabrasive particle for polishing a layer of a semiconductor device. 22.The method according to claim 19, wherein the semiconductor device isselected from the group consisting of a copper layer, a low-k dielectriclayer having a dielectric constant k lower than 3.9, a photosensitivelayer, and a semiconductor wafer substrate.